The physical size of digital computer systems has been the subject of a substantial development effort for a number of years. The space occupied by such computer systems has decreased markedly, as a result of a dramatic reduction in the size and power dissipation of the various components that make up the system. In particular, the large-scale integration of central processor units and memory units and the reduction in size of disk sub-systems have materially reduced the aggregate physical volume of the units that make up the overall system.
Even so, the "packaging" of these units in a minimum physical volume remains a challenge to the designers of these systems. As the volume decreases, one encounters increased difficulties and expenses in maintenance and repair due to the limited space and greater concentration of components within such systems. Further, the extraction of internally generated heat becomes more difficult, a significant problem in view of the relatively low temperatures that must be maintained for reliable performance of the various sub-units of such computer systems. The temperature problem is aggravated by the fact that one reason for small sizes is to acquire more freedom in the location of computer systems in general and, in particular, to be free to place them in areas that do not have special climate-control facilities. Also, the placement of such computer systems in office and other such environments require that the system be substantially quiet.